Thin protein films of gelatin molecules grown on flexible substrates have been utilized to fabricate moisture-induced energy-harvesting devices, which work as self-biased sensors. Adsorbed water molecules from ambient moisture generate protons inside the film. A proton transfer path is formed through the hydrogen-bonded water molecules with protein around 55% relative humidity condition, and the protons are transferred due to the gradient of absorbed water molecules within the protein films. The devices are capable of harvesting electric power up to 5.5 μW/ cm 2 with an induced voltage of 0.71 V. Our findings not only provide a futuristic clean power generation concept from protein film as flexible power generator but also demonstrate the use of the energy-harvesting devices as self-biased electronic sensors for various flexible and wearable applications. The devices showed exceptional performance as humidity sensors and have been used for flexible healthcare applications, such as continuous monitoring of breathing pattern and lateral mapping of moisture levels at the finger tip for monitoring the wound healing process. Nevertheless, the diode-like response of the devices with humidity has been found to be suitable as a self-biased humidity-controlled electronic switch.

Meticulous surface engineering of layered structures toward new functionalities is a demanding challenge to the scientific community.Here, we introduce defects on varied MoS 2 surfaces by suitable doping of nitrogen atoms in a sulfur-rich reaction environment, resulting in stable and scalable phase conversion. The experimental characterizations along with the theoretical calculations within the framework of density functional theory establish the impact of nitrogen doping on stabilization of defects and reconstruction of the 2H to 1T phase. The as-synthesized MoS 2 samples exhibit excellent dye removal capacity in the dark, facilitated by a synergistic effect of reactive oxygen species (ROS) generation and adsorption. Positron annihilation spectroscopy and electron paramagnetic resonance studies substantiate the role of defects and associated sulfur vacancies toward ROS generation in the dark. Further, on the basis of its ample ROS generation in the dark and in the light, the commendable antimicrobial activity of the prepared MoS 2 samples against fungal pathogen Alternaria alternata has been demonstrated. Thus, the present study opens up a futuristic avenue to develop newer functional materials through defect engineering by suitable dopants toward superior performances in environment issues.

Careful tuning of formation (calcination) temperature of Sr(2+) doped BiFeO(3) multiferroic ceramics results in tailorable particle morphologies ranging from spherical to pillar-like. Based on the minimization of Gibb's free energy approach, the dominant homogeneous mechanism for particle growth is suggested. The chemical substitution of a trivalent ion (Bi(3+)) by a divalent ion (Sr(2+)) causes the transformation of certain fraction of Fe(3+) to Fe(4+) and/or the appearance of oxygen vacancies. This has been respectively proved by the analysis of XPS and refinement of neutron diffraction data. Although significant modification in the particle morphology is observed, the crystal unit cell remains rhombohedral with a R3c space group but interesting variations in physical properties are achieved. O-vacancies induced strong and sharp photoluminescence activity in the IR region, similar to ZnO, is reported for the first time. This observation opens up a new application for multiferroic ceramics. SQUID M-H data confirms the straightening of the canted spin structure of BiFeO(3), which in turn results in magnetism similar to ferromagnetic materials. Findings of the magneto-dielectric effect are also discussed to claim the multiferroic nature of the sample.

We have developed low-voltage (<2 V) flexible organic field-effect transistors (OFETs) with high carrier mobility using gelatin as a moisture-induced ionic gate dielectric system. Ionic concentration in the gelatin layer depends on the relative humidity condition during the measurement. The capacitance of the dielectric layer used for the calculation of field-effect carrier mobility for the OFETs crucially depends on the frequency at which the capacitance was measured. The results of frequency-dependent gate capacitance together with the anomalous bias-stress effect have been used to determine the exact frequency at which the carrier mobility should be calculated. The observed carrier mobility of the devices is 0.33 cm2/Vs with the capacitance measured at frequency 20 mHz. It can be overestimated to 14 cm2/Vs with the capacitance measured at 100 kHz. The devices can be used as highly sensitive humidity sensors. About three orders of magnitude variation in device current have been observed on the changes in relative humidity (RH) levels from 10 to 80%. The devices show a fast response with a response and recovery times of ∼100 and ∼110 ms, respectively. The devices are flexible up to a 5 mm bending radius.

We report on the synthesis and UV–vis photodetection application of p-type MoO2 nanostructures (NSs) on Si substrate. β-MoO2 NSs have been synthesized from previously grown α-MoO3 structures/n-type Si via a hydrogenation process at 450 °C. After hydrogenation, the α-MoO3 structures were completely converted into β-MoO2 NSs without the presence of sub-oxidized phases of molybdenum oxide. The as-grown NSs exhibited very good p-type electrical conductivity of ≈2.02 × 103 S–cm−1 with hole mobility of ≈7.8 ± 1.3 cm2–V−1–Sec−1. To explore optoelectronic properties of p-type β-MoO2 NSs, we have fabricated a p-MoO2/n-Si heterojunction photodetector device with Au as the top and Al as the bottom contacts. The device exhibits peak photoresponsivity of ≈0.155 A W−1 with maximum detectivity ≈1.28 × 1011 cm–Hz1/2–W−1 and 44% external quantum efficiency around ≈436 nm, following the highest photoresponse (Iph/Id ≈ 6.4 × 102) and good response speed (rise time ∼29 ms and decay time ∼38 ms) at −1.5 V. Importantly, this device also shows good self-powered high-speed (rise time ∼47 ms and decay time ∼70 ms) photodetection performance with peak responsivity and detectivity of ≈45 mA W−1 and ≈4.05 × 1010 cm–Hz1/2–W−1, respectively. This broadband UV-visible light detection feature can be attributed to the coordinated effects of MoO2 band-edge absorption, interfacial defects and self absorption in Si. The photodetection behavior of the device has been understood by proposed energy-band diagrams with the help of an experimentally derived work function, band gap and valence band maximum position of MoO2 NSs.

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Organic field-effect transistors (OFETs) with hexagonal barium titanate nanocrystals (h-BTNCs) in amorphous matrix as one of the bilayer dielectric systems have been fabricated on a highly flexible 10 μm thick poly(ethylene terephthalate) substrate. The device current and mobility remain constant up to a bending radius of 4 mm, which makes the substrate suitable for wearable e-skin applications. h-BTNC films are found to be highly temperature-sensitive, and the OFETs designed based on this material showed ultraprecision measurement (∼4.3 mK), low power (∼1 μW at 1.2 V operating voltage), and ultrafast response (∼24 ms) in sensing temperature over a range of 20−45 °C continuously. The sensors are highly stable around body temperature and work at various extreme conditions, such as under water and in solutions of different pH values and various salt concentrations. These properties make this sensor unique and highly suitable for various healthcare and other applications, wherein a small variation of temperature around this temperature range is required to be measured at an ultrahigh speed.